TS 320 
.U6 
1920 
Copy 2 



n No. 361 



NOTES ON 
INSPECTION 



OF 



STEEL FORGINGS 



NAVY DEPARTMENT 

BUREAU OF ENGINEERING 




> 






WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1920 



N. S. E. Form No. 361 



NOTES 
INSPE 



OF 



STEEL FORGINGS 



NAVY DEPARTMENT 

U,"*, BUREAU OF STEAM ENGINEERING 




WASHINGTON 

GOVERNMENT PRINTING OFFICE 

1920 






S7 it D* 

OCT 29 J923, 



30-Ztfa#l 



TABLE OF CONTENTS. 



Paragraph. Page. 

1. Contract and specifications 7 

2. Manufacture of ingots 7 

3. Inspection of ingots 7 

4. Process of manufacture of forgings 8 

5. Marking forgings for identification 8 

6. Heat treatment. 8 

7. Test specimens 9 

8. Testing 9 

9. Metallographic specimens 9 

10. Inspection during machining 10 

11. Finish inspection of crankshafts 10 

12. Finish inspection of hollow-bored shafts 12 

13. Final inspection 15 

14. Small forgings 16 

15. Ghost lines i6 

16. Stamping and weighing 16 

162317—20 (3) 



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INTRODUCTION. 



The following notes on the inspection of steel forgings have been 
compiled from methods in use in various inspection offices, and while 
they are not intended to prescribe a procedure to be followed in the 
inspection of this material they may be found useful to assistant inspec- 
tors not having had long experience. 

(5) 



INSPECTION OF STEEL FORGINGS. 



1. CONTRACT AND SPECIFICATIONS. 

The assistant inspector should thoroughly familiarize himself with the 
requirements of the contract or order and the Navy Department specifica- 
tions in accordance with which the material is to conform. Any apparent 
inconsistency or condition in the contract or order which is not entirely 
clear should be brought to the attention of the Inspector in charge of the 
district, and instructions obtained before the inspection is begun. 

2. MANUFACTURE OF INGOTS. 

The use of acid or basic open-hearth furnaces and electric furnaces is 
approved. When the furnace charge, consisting of pig-iron, steel 
scrap and a suitable flux, has been reduced to the proper carbon 
contents, determined by means of ladle tests taken at varying inter- 
vals, it is tapped and the molten steel drawn off in a ladle or ladles, 
from which it is poured, usually from the bottom, into ingot molds. The 
ingot molds are generally so formed as to produce ingots of cylindrical 
form with fluted sides, or of square cross section. In each case the molds 
are tapered to insure ready withdrawal. In some cases the metal is 
poured into the top of the molds, called "top poured; " in others, through 
runners into the bottom of the molds, whence it rises to the top, called 
"bottom poured;" and less frequently into molds so arranged that the 
metal is subjected to hydraulic pressure while in the partial liquid state, 
called fluid compressed. After solidifying, the ingots are removed from 
the molds. If practicable, heat may be saved by transferring the hot ingot 
to the forge furnace, and after soaking it may be forged. 

3. INSPECTION OF INGOTS. 

Provided ingots are not charged (hot) direct from the molds into the 
forging furnace they may be inspected for defects and the data obtained 
recorded. The most common defects to occur in ingots are cooling 
cracks and defects in the surfaces caused by the splashing of the molten 
metal. The removal of these defects by chipping is permitted and the 
extent to which chipping may be done is usually covered by the speci- 
fications. In all cases the following data should be recorded: 

(a) Name of the manufacturer. 

(b) Heat number and serial number of ingot. 

(c) Form of mold used, square, fluted sides, number of sides, etc. 

(d) Dimensions and weight (in order to determine the discard). 

(e) Kind of furnace used (acid or basic) (open-hearth or electric). 
(/) How poured (top, bottom, or fluid compressed). 

(g) Approximate weight of ingot mold employed. 
If the firm manufactures its own ingots, the inspector should become 
acquainted with the process employed. 

(7) 



8 

The use of sand-cast ingots is prohibited. Ingots so cast are inferior 
to chilled cast ingots, since forgings made from them are liable to con- 
tain ghost lines, areas of segregated nonmetaliic inclusions and other 
defects. See paragraph 15 for further comment in this regard. 

4. PROCESS OF MANUFACTURE OF FORGINGS. 

Forgings are made both by hammer and hydraulic press, the larger 
ones by the latter method, since in addition to the better facility for 
producing the forging, a more thorough working of the metal is obtained. 
The ingots, especially nickel steel, should be carefully warmed before 
charging into a hot furnace. They are usually charged horizontally 
and with the top of the ingot protruding from the furnace door, all 
space not occupied by the ingot in the doorway being bricked up. If 
practicable the ingot should be charged into the furnace, permitting 
not over 20 per cent to remain cool. A chuck is attached to this cool 
top of the ingot by means of which the ingot is carried to the press or 
hammer and turned while in the process of being forged. In case of 
small forgings tongs may be employed. The ingot should be heated to 
about 2,200° F. and soaked at that temperature a sufficient time so that 
when forged the hot end does not become extremely concave or convex. 
Concave ends may be formed by not permitting sufficient soaking, thus 
the center being colder and consequently harder than the surface. Con- 
vex ends may be formed by permitting the surface of the ingot, which 
has been properly heated, to chill before forging is begun or to cool dur- 
ing foiging. 

In the forging of large shafts, etc., it may be necessary to reheat the 
partly forged ingot several times before forging can be completed. 

When forged to a predetermined size the required amount of bottom 
discard is calculated, measured, and cut off. 

The amount of top discard including the tong-hold should be cal- 
culated or weighed in order to determine that the required amount has 
been removed. Navy Department specifications prescribe a minimum 
reduction of area of the ingot and forging. This required reduction of 
area is usually 4 to 1 excepting for palms and flanges. 

5. MARKING FORGINGS FOR IDENTIFICATION. 

As soon as forged each forging should be stamped with a forging num- 
ber supplied by the manufacturer, which should be a key to the ingot 
number, and this record kept by the inspector. The inspector should 
stamp the end of the forging "USN" and "M" (muzzle or top) or "B" 
(breech or bottom) to indicate the relative position in the ingot. These 
marks should be placed near the forging number. 

6. HEAT TREATMENT. 

The heat-treating equipment should be of an approved design and such 
as to evenly heat and cool the forging. The pyrometers should be so 
installed as to enable the inspector to satisfy himself that the forging is 
being uniformly treated. Uniformity of temperature may be noted by 
the color, and if the forging is not of a uniform color before quenching, 
it should be returned to the furnace and reheated. 



7. TEST SPECIMENS. 

Upon the submission of the forging after heat treatment, test specimens 
should he located in accordance with the specifications of the contract 
or order. B and M test bars are taken from prolongations provided on 
each end of forgings. The diameter of these prolongations should be 
at least equal to the greatest rough diameter of the forging except 
palms and flanges. In crank shafts, the section withstanding the greatest 
stresses is represented by the W and X bars and care should be exercised 
to guard against the drilling of holes or otherwise treating tbe shaft in 
order to produce a special beat, treatment of the metal from which these 
test bars are to be taken. In all cases each specimen should be stamped 
with the forging number, USN, arid letters indicating the location from 
where taken, that is, MI, MO, BI, etc. Specimens for metal lographic 
examination need not be located until after the physical tests have been 
made. The removing of test pieces may be accomplished by trephinirig, 
slotting, or otherwise machining. Burning off of test pieces should not be 
permitted. 

8. TESTING. 

The assistant inspector should identify each test specimen after machin- 
ing, and check up the dimensions to determine that they have been ma- 
chined uniformly to tbe required diameter, and that the punch marks are 
exactly 2 inches apart. The surfaces of all tension test specimens should 
be free from tool marks and scratches. The excuse that poorly prepared 
test specimens are to the advantage of the Government should not be 
accepted, since accurate determination of the condition of tbe steel in 
the forging is desired as well as the information as to whether the steel 
is in full conformity with tbe requirements of tbe specifications. In 
case the inspector does not actually operate the testing machine, be should 
witness the operation and satisfy himself that the machine is being op- 
erated in a proper manner and that correct readings are obtained . 

After breaking, each tension test piece should be examined for flaws 
appearing along its walls, as well as the grain structure as indicated by 
the fracture, and the assistant inspector should make note of the results 
of this examination. 

The measurements for elongation and reduction of area should be taken 
by the assistant inspector. 

The bending test may be made under a hammer, press, or by means of 
the testing machine. Specimens for bending tests should in all cases be 
approximately of the cross section required by the specifications. Bend 
specimens under £ inch thick should be rejected. 

Drillings for chemical analysis should be taken from that end of 
the forging representing the top of the ingot and are usually obtained 
from the bend test specimen, but may be taken from one of the "M" 
tension bars. 

9. METALLO GRAPHIC SPECIMENS. 

In case metallographic specimens are required the broken test speci- 
mens bearing the stamps necessary for identification and the additional 
specimens required should be properly marked and forwarded to the 
Engineering Experiment Station at Annapolis. These specimens should 
be accompanied by form N. S. E. 76, with entries to show the results of 
the chemical analysis and physical teste. 

162317—20 2 



10 

10. INSPECTION DURING MACHINING. 

Inspection during machining should be made to detect seams, ghost 
lines, etc. These defects may often be detected by the breaking of the 
chip, and such inspection will also prevent chipping and peening or the 
welding of flaws. As the machining of the forging proceeds it often 
becomes necessary to transfer stamps. In all cases the stamps should be 
transferred to the machined surface before the original stamp is machined 
off. The transfer of identification stamps should be made by or in the 
presence of the assistant inspector. 

11. FINISH INSPECTION OF CRANE: SHAFTS. 

(a) A method which has been found satisfactory in the inspection of 
submarine crank shafts is as follows: Support the shaft on V -blocks of 
equal height placed under the main bearings Nos. 2 and 7, the blocks 
resting upon the surface plate. Measurements should be made with a 
surface gauge to insure that the shaft lies parallel with the surface plate 
and that there is no tendency to sag. Steps should be taken to insure 
that this alignment is maintained during subsequent inspection. The 
surface of the shaft should then be carefully examined for all defects 
such as deep scratches, small cracks, undercut fillets, etc. , and the loca- 
tion of the oil holes should be checked. The diameter of each crank 
pin and each bearing should be measured by micrometer at points at right 
angles to each other for variation in diameter, and for deviation from 
exact roundness. The maximum variation in diameter rarely exceeds 
0.002 inch. 

(b) Linear dimensions. — With a machinists' scale the length of each 
crank-pin bearing and main bearing and the width and thickness of the 
webs and thickness and diameter of the flanges should be measured. 

(c) Inspection of throws.— The location and dimensions of the key-ways 
should then be checked. As the bolt holes in the afterflange are 
drilled to a template furnished the manufacturer by the contractor and 
are reamed to suit the reversing mechanism after assembly, these holes 
need be checked only as to location with respect to the crank pins. The 
surfaces of the holes should be examined for possible defects in the flange. 
The accuracy of the angles should be checked by means of a dial gauge 
graduated to .001 inch. The shaft should be revolved until the parallel 
web surfaces of crank pin B , sketch A , are exactly at right angles to the sur- 
face plate. This alignment should be made with a machinist's square. 
The dial should then be adjusted so that a reading taken when moving 
the gauge over crank pin A gives a reading of about .050 inch. Readings 
should then be taken on crank pins 5, 3, and 4. These readings will 
probably be about as follows: .042 inch, .056 inch, .061 inch. The shaft 
should then be revolved until parallel surfaces of crank webs C are 
exactly at right angles to the surface plate, and without changing the 
gauge adjustment, reading should be taken on crank pins 1, 6, 2, and 5. 
These readings will probably be about as follows: .048 inch, .034 inch, 
.060 inch, .053 inch. The maximum error in angles is the difference 
between the least reading and the greatest, which in the above case is 
.061 — .034 inch, which equals .027 inch. 

(d) The above method should not be employed until after the web 
surfaces have been tested for parallelism with the planes passing through 
their respective pins and the journals. This may be accomplished by 



11 

placing each pair of pins in a position parallel with the surface plate 
and by means of the surface gauge determining that the web surface is 
parallel also. 

(e) If it is not practicable to determine that the web surfaces are 
parallel, or if for any other reason it is desired, the following method 
may be employed : 

The shaft should be revolved until the parallel web surfaces of crank 
pin B, sketch A, are approximately at right angles to the surface plate. 
A machinist's square may be used to obtain this alignment. The dial 
ehould then be adjusted so that a reading taken when moving the gauge 
over crank pin A, which is No. 2, gives a reading of about 0.050 
inch. The machinist's square should then be removed and the shaft 
revolved sufficiently to cause the top of pin 2, and 3 corresponding to C, 
to lie in the plane parallel with the surface plate. Readings of the 
gauge for pins 2 and 3 are taken, and for illustration assume these to 
be 0.056 inch and the readings for pins 5 and 4 to be 0.042 inch and 
0.061 inch, respectively. The shaft should then be revolved approxi- 
mately 120°, and until pin 2 in its new position and with the adjustment 
of the gauge unchanged gives a reading of 0.056 inch. Assume the 
reading of pins 1, 6, and 5 to be 0.048 inch and 0.070, respectively. 
In like manner pin 3 should be revolved to the position indicated by 
A in the sketch, and in such a position that the gauge, still at its original 
adjustment, registers 0.056 inch. The readings of pins 1 and 6 should 
then be made. These may be assumed to be 0.053 inch and 0.048 inch, 
respectively. The maximum error in angles is the difference between 
the least and the greatest readings, which in the above case would be 
0.070-0.042 inch, which equals 0.028 inch. 

(/) Calculations. — The maximum error in angles is generally given 
in degrees and is usually about 0.5°. In order to determine this value. in 
gauge readings in inches the following formula may be employed, assum- 
ing: 

R = Radius of throw, inches=7.0. 

D = Angle of pins, degrees= 120.0. 

D / =Maximum angle of pins, degrees= 120.5. 

X = (cosine D' — cosine D)XR- 
In the above case the following results are obtained: 

Cosine D / =cosinel20°.5=sine 30°.5=.50754. 

Cosine D =cosine 120°.0=sine 30°. 0=. 50000. 

R=7.0 inch. 

X=.00754X7.0=.0527S inch or approximately .053 inch. 
When the difference between the least and the greatest gauge reading 
is less than .053 inch the error is less than 0.5°. The readings taken 
before revolving the shaft show that angles "D" and "E" are equal but 
do not show that they are 120°. Measuring angle "F" together with 
"D " or "E" proves that all the angles are approximately 120°. 

(g) Length of stroke. — The throw of the crank should be measured 
by a height gauge, the web being at right angles to the surface plate. 
The error in stroke should be measured by revolving the shaft until the 
parallel web surfaces of each of the pins A, B, and C are successively at 
right angles to the surface plate, and then reading the gauge as shown 
in sketch B. All readings should be taken with the same setting of the 
gauge. The readings obtained will probably vary about as follows: 
.068, .059, .071, .078, . 063, and .0S2 inch. The maximum error in stroke 



12 

is the difference between the least and greatest reading, which in this 
case would be 

.082 inch -.059 inch=.023 inch. 

The maximum error permitted in stroke is usually .030 inch. 

(h) Variation of axes. — The variation of axis of any one main bearing 
from the axis of shaft when measured by revolving shaft on V-blocks may 
be obtained by adjusting the dial gauge to the bearing under test, revolving 
the shaftin the V-blocks and noting the deflection of the gauge. 

(i) Inspection of coupling bolts, flanges, etc. — Submarine crank shafts 
usually consist of two sections. After the above tests have been made 
these sections are disconnected. The fit of the coupling bolts, which is 
a driving fit, is indicated by the effort required to remove the bolts. After 
the section has been disconnected the surfaces of the coupling flanges 
should be examined to discover evidences of piping, ghost lines, etc. 

12. FINISH INSPECTION OF HOLLOW-BORED SHAFTING. 

(a) In order to provide the required strength with a minimum of 
weight, shafts are usually bored as follows: Line shafts are bored the 
same diameter throughout; stern-tube shafts are bored with the large 
hole extending nearly to the after end; and propeller shafts are bored 
with a large bore from the end upon which a collar about lh times the 
diameter of the shaft has been left nearly to taper for propeller. To 
bore the small holes the last two shafts are turned end for end and the 
small holes are then bored to meet the large hole. The small hole 
should be first bored smaller than finished dimensions, say 2 inch 
diameter for a 3-inch hole, then measurements taken and shaft centered 
by the large hole so that when the small hole is then bored it will be 
concentric with the large hole. Propeller shafts generally have small 
holes at each end. After boring the large hole and the small hole in 
one end, the end of the shaft bearing the collar is heated and the collar 
reduced by forging until the hole is nearly closed. The small hole is 
then bored in a manner similar to the boring of the small hole in the 
opposite end of the same shaft. This closing in of the shaft ends should 
in all cases precede final heat treatment and-tests. 

(6) Inspection of surface. — Upon the submission of the shafts, finish 
machined or rough machined as required by the order or contract, such 
shafts should be surface inspected for flaws, seams, black spots, ghost 
lines, etc. The diameters of rough machined shafts may be measured 
by means of calipers. Diameter of finish machined shafts should be 
determined by means of micrometers. Lengths should be checked 
by the use of a steel tape. 

(c) Inspection of bore. — The bore should be carefully inspected for 
uniformity, concentricity, and flaws, such as piping, etc., and that the 
proper boring cutter has been used to cut the proper angles between the 
large and small bores. The bores of propeller shafts should be inspected 
before closing in. After successfully passing the above inspection the 
hollow-bored shafts should be placed in a lathe or on suitably designed 
rolls, measurements taken at ends of the shaft to determine thickness of 
shaft walls, and the bore indicated by means of an apparatus similar to 
the sketches shown. 



13 



J2/&/ Gau ge. 




\ Surf@c% of /&y~Quf tab/e. 



Sketch A. 




Sketch 8. 



14 

3 '1 ption of sketch, of electrical indicator. 

The shaft the bore of which is to be inspected is placed in a lathe, chucked 
at one end and supported near the other end by a carefully adjusted steady 
rest, in such a manner as to cause the shaft to run true with the outside. 

The indicating apparatus consists of a pipe 16 feet long and of sufficient 
outside diameter to prevent sagging and small enough to pass through the 
reduced bore of the shaft. One end of this pipe is clamped securely to a 
"slide rest" and on the other end is attached a finger or lever. This lever is 
so pivoted that it may be adjusted parallel with the pipe when passing through 
the reduced bore, and can be made to assume a transverse position, shown 
in the sketch, by means of a wire running through the pipe, the wire being 
held taut and secured so as to hold the lever firmly fixed. 

The tip of the lever is insulated from the pipe and an insulated wire runs 
from this tip through the pipe to a switch of the lighting circuit. The other 
side of the circuit is grounded to the lathe bed as shoion, both switches being 
closed when the apparatus is in use. 

The pipe is marked off on the outside every 2 feet, longitudinally from 
the lever tip in its fixed position, so as to determine just where measurements 
are taken; and the intermediate points are determined by a rule laid along 
the pipe at the end of the shaft. With a 16-foot pipe, measurements can be 
made up to about 14 feet inside the shaft. 

By means of the slide rest, the apparatus is moved to any desired position 
in the shaft, working first from one end and then the other end of the shaft, 
if it is more than 14 feet long. The transverse feed of slide rest provides for 
mdvement of the apparatus transversely, and as soon as lever tip touches 
wall of the shaft, the electric lights shown in the circuit flicker or light up. 
The travel of the lever tip should be in the horizontal plane of the axis of the 
shaft for accurate measurements; but for practical purposes the eye is accurate 
enough vjhen adjusting the pipe in clamps of slide rest, with the free end of 
pipe just entered in the shaft. Two scales are laid on transverse bed of slide 
rest in order to measure the exact transverse movement of the apparatus. 

Use of apparatus. 

The different quadrants are indicated on the end of the shaft by the letter s 
"A," "B," "C," and "D"; apparatus being secured in proper position 
in slide rest and moved into shaft to proper position for first measurements 
of bore. The lever is then hauled back and secured in position. 

With shaft slowly revolving, using transverse feed of slide rest, contact point 
is moved until it touches the surface of the bore, when the lights in the circuit 
will flash, indicating that a "high spot" has been touched. The point on the 
circumference which has been touched is noted, and is indicated by a mark on 
the end of the shaft, and the scale reading on slide rest is taken. Then the 
shaft is turned so that the "high spot" detected is 180° from the contact point 
of the lever. With the shaft fixed in position, the apparatus is again fed trans- 
versely until the lights flash. The scale reading on the slide rest is again noted 
and the difference between the two readings shows the movement of contact 
point. One-half of this movement is the amount the axis of the bore is eccentric. 

When more than a slight eccentricity is noted, careful measurements of the 
lore should be taken, each 2 or 3 inches in length, and in each quadrant. 
Ordinarily indications are made only every 2 feet of length. 

Comment. 

The above apparatus should only be used when the boe of the shaft has been 
carefully searched with an electric torch and it has been found that the bore 




r tfco/e 



SJ-pJ-ionartj 
Scale 



~T 22o f V Lighting 



S.L 



circui-f- 



\ 



■■■&-. 



I Ground J-c 
\/laJ-he bed 





Moving «o/« *§£%?"* 



162317—20. (To face papo 14.) 



ELECTRICAL INDICATOR 



15 

has no serious defects or irregular cutting on the part of the boring tool. 
Particularly with a shaft which has u closed-in" ends the bore should be care- 
fully examined before the ends have been closed in, since it is very difficult to 
examine the bore through the small hole after the end is closed in, and in this 
case the above apparatus might not show up a local flaw, hump, or spiral 
groove in the bore. 

When using the apparatus care must be taken not to start the 16-foot pipe 
vibrating, as the free end will easily vibrate over an inch, and take a minute 
or two to come back to rest. Also, moisture must be eliminated at the electric 
contact point for accurate readings. 

The apparatus appears accurate for measurement of eccentricity of the bore 
at any desired point, provided the cross section at that point is a circle. If the 
cross section is elliptical or otherwise irregular, it will be necessary, in order 
to show up the true form of the bore, to take a large number of readings, which 
would require a great deal of time. 

Mechanical indicator. 

A sketch of a mechanical indicator which has been used is shown on the 
opposite page. 

(d) Tolerance in eccentricity. — In the absence of other instructions an 
eccentricity of the axis of the large bore of rough machined shafts of -fa 
inch and an eccentricity of the axis of the small or reduced bore of rough 
machined shafts of xs inch is generally permitted. A variation in wall 
thickness measured at points 180° apart of the circumference corresponds 
to twice the eccentricity of the axis of the bore . A variation in wall thick- 
ness of -rg- inch, measured 180° apart of a circumference, corresponds to ^ 
inch eccentricity of the axis of the bore. The length of bores should con- 
form to the requirements of the drawings, except for propeller shafts with 
closed-in end . After boring it is impossible to forge down the open end 
so that the taper and bore will exactly agree with the drawing. In no case 
should the large bore extend farther than specified, since the shaft is 
tapered for the coupling and the propeller, and the strength would thus 
be impaired. The maximum length of the large bore should be that 
shown on the drawing. 

(e) Tolerance of diameter of bore. — The tolerance of diameter of bore 
is usually stated on the blue print. The provisions of the General Speci- 
fications for Machinery E3, May 1, 1919, in this regard are as follows: 
"The tolerances in diameter of bore will be f inch under size and fg- inch 
over size." 

(/) Straightening shafts. — Any working below forging heat should be 
very carefully watched as initial stresses are liable to occur at the point 
where bending is done. Shafts that have been warped or bent slightly 
while undergoing heat treatment may be straightened by reheating to 
not over 700° F. In case such forgings are heated over 700° F. complete 
retests should be required. 

13. FINAL INSPECTION. 

(a) The assistant inspector must be assured by actual checking that 
all dimensions are in accordance with the requirements of the specifica- 
tions of the contract or order, and permitted tolerances, and that in the 
case of rough-turned shafting there is sufficient metal for finish machin- 
ing. Careful examination of all surfaces must be made for hair-line 
cracks, streaks, and ghost lines. 



16 

14. SMALL FOBGINGS. 

The inspection of small forgings should be conducted in the same 
manner as large forgings except that tests may be taken to represent 
a lot as defined by the specifications. Metal for test should be pro- 
vided by the manufacturer on several forgings in each lot in order 
that the assistant inspector may select such forgings as he may desire 
from which to obtain test specimens. In lieu of providing extra metal 
for testing, the manufacturer may request the assistant inspector to 
select a forging for test. 

15. GHOST LINES. 

Ghost lines sometimes exist in forgings, and in all inspections of ma- 
chined surfaces of forgings care should be exercised to detect such de- 
fects, and if they exist to report to the Inspector in order that a special 
investigation may be conducted to establish their extent. 

Due to the different temperatiue of solidification, there is a tendency 
of certain nonmetallic constituents, such as sulfides, silicides, etc., to 
gather into areas in an ingot as the metal becomes solid. As the steel on 
cooling passes from the austenitic to the sorbitic and thence to the pear- 
litic stage, ferrite is freed and each particle of nonmetallic substance is 
surrounded by pure ferrite. If the nonmetallic particles are numerous 
and due to forging, the area has been elongated, aline or streak of metal 
of color unlike that surrounding it appears. This line has been given the 
name of ghost line. 

As stated, the nonmetallic substances are surrounded by free ferrite, 
drawing such ferrite from the surrounding pearlite and ferrite, thus in- 
creasing the carbon content of the metal adjacent to the ghost line, with 
a resulting hardening of same. This increasing of the carbon content 
of the steel surrounding a ghost line and thus rendering it harder ex- 
plains the jumping of the tool and the consequent ridge on the forging. 

Forgings made from ingots cast in metal molds are less likely to de- 
velop ghost lines than those made from ingots cast in sand. The 
longer time the metal remains liquid in the ingot mold the greater the 
segregation of impurities with resulting ghost lines. 

16. STAMPING AND WEIGHING. 

After final inspection has been completed and it has been determined 
that the forging is in accordance with the requirements of the contract 

or order it should be stamped "USN" and ^7"^ adjacent to the forg- 
ing number. The forgings should also be stamped with identification 
numbers or letters if such are required by the order. . Crank shafts should 
be stamped on the face of one of the webs. Care should be exercised 
that stamping of finished forgings is not done on bearing surfaces. In 
all cases forgings should be weighed by the assistant inspector and note 
that weight was checked made on the Report of Material Shipped. 

CONCLUSION. 

The foregoing is an outline of a procedure in the inspection of this 
class of material. In general, since the contractors furnish the means 
and the labor necessary to establish that their product is satisfactory, 
their methods of checking dimensions, alignments, etc., should be em- 
ployed, provided there be no reason to doubt the accuracy of the 
results obtained thereby. The inspector has the right to recheck by 
his own methods, but should exercise this right only in case conditions 
obtain during inspection under the contractor's methods which render 
such action advisable. 

o 



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